If you do, they're now void and must be removed, thanks to the new Consumer Review Fairness Act. Non disparagement clauses, which businesses used to go after consumers who gave them bad reviews on websites such as Yelp, have been long hated. Now they're illegal. For example, Kirschenbaum's contracts including those clauses and now they are informing their customers they are void.
Have you ever added a non disparagement clause to your contracts? If so, what will you do to combat bad online reviews now?